Multichamber directional solidification vacuum casting furnance

ABSTRACT

A vacuum melting and casting apparatus for directional solidification of metallurgical castings which employs a single traveling melting chamber and a plurality of molding chambers. By successively coupling the melting chamber with one of the mold chambers at a time, the cast components may be melted and poured under vacuum and thereafter cooled in mold chambers under isolated vacuum conditions so that the melting equipment is not retained in an inactive status during the relatively long directional solidification cycle.

United States Patent [54] MULTICHAMBER DIRECTIONAL SOLIDIFICATION VACUUM CASTING FURNANCE g and casting apparatus for tallurgical castings which emg chamber and a plurality of ssively coupling the melting the mold chambers at a time, the cast 258151 254; 266/1);- 2 components may be melted and poured under vacuum and thereafter cooled in mold chambers under isolated vacuum conditions so that the meltingequ inactive status during the relative] tion cycle.

[56] References Cited UNITED STATES PATENTS ipment is not retained in an y long directional solidificat0l4255 12/1961 Bussardetal...... 266/34VUX PATENTED M82419?! 3.601.179

SHEET 1 [1F 3 INVENTOR 1 KENDR/CK C. TAYLOR ATTORNEY PATENTEU AUG24 I971 SHEET 3 OF 3 M. W MM V [Q E WK M wm m R n o m x MULTICHAMBER DIRECTIONAL SOLIDIFICATION VACUUM CASTING FURNANCE The invention relates to vacuum melting and casting apparatus, and more particularly relates to vacuum metallurgical apparatus for casting directionally solidified alloy' components.

In the manufacture of directionally solidified cast articles,

the mold is heated to a high temperature prior to and during pouring of the molten metal into the mold. The mold is held at a selected temperature for a predetermined extensive period of time after pouring through the use of a mold heater which is positioned about the mold. In addition, a temperature gradient is established during solidification from one end of the mold to the other along a transverse solid-liquid front which is controlled to move at a predetermined selected rate from one end of the mold to the other. By minimizing grain boundaries,

especially in the case of single-crystal castings, one is able to obtain improved high-temperature engine parts. After pouring, a usual cooling time to effect directional solidification for a typical component suchas 'a turbine blade, is in the range of 200 to 300 minutes. g

' As is well known today, the melting and refining. of metals and alloys under vacuum prevents atmospheric oxidation and permits removal of deleterious gases, such as oxygen, hydrogen and nitrogen. lnaddition, casting under vacuum further reduces atmospheric contamination and, when directionally solidified casting under vacuum is combined with vacuum melting and refining, high-temperature precision castings may now be produced of a quality heretofore not obtainable. Up to now, directionally solidified castings have been made in single-unit vacuum furnaces in which the casting is conducted in the same chamber as the melting or, in some instances, the mold chamber or locker is directly attached to the melting chamber as has been indicated above. A typical time period for solidification of a directionally solidified cast part can extend approximately 300 minutes. On the other hand, an

average time for melting a cold slug of metal after it has been charged into the crucible and then pouring the molten metal into the mold may take a total of perhaps to minutes.

Thus, where it is desired to both melt and cast in a vacuum, previous designs for such vacuum equipment have been quite costly to the foundry and prohibitive in terms of production capacity..lhat is, the extremely long solidification cycle relativeto the melting period would dictate that prior vacuum melting furnaces stand by inactively during the solidification period. n

It is therefore 'an object of this invention to provide a directional solidification vacuum casting apparatus in which a single traveling melting chamber may be successively coupled to one of a plurality of individual vacuum molding chambers whereby melting, pouring and thereafter cooling all under vacuum, may be accomplished in an efficient cycle without breaking vacuum and without any necessity whatsoever of the melting equipment being held inactive during the solidification period.

Another object of this invention is to provide a directional solidification casting system which yields maximum reliability at-minimum equipment investment.

Still another object of this ';invention is to provide a directional solidification casting apparatus in which the life of the refractory lining of the furnace or crucible is materially extended. That is, an attendant benefit to rapid sequence vacuum casting is the maintenance of a relatively even temperature of the furnace itself without the. substantial fluctuaminimizes flaking and cracking of the furnace refractory,

, there is minimal inclusion ofrefractory particles in subsequent castings. Furthermore, by avoiding the necessity of breaking vacuum to the melting chamber after pouring, oxygen cannot reenter the furnace interior and is thereby prevented from being retained by the refractory lining.

Other objects of this invention are to provide an improved device of the character described which is sturdy in construc disposition with one of the mold chambers;

FIG. 4 is a fragmentary bottom perspective view of the furnace chamber platform showing the lateral shifting carriage;

FIG. 5 is a fragmentary bottom perspective view thereof I showing the longitudinal drive;

FIG. 6 is a sectional view taken along lines 6-6 of FIG. 4.

Referring now in greater detail to the drawings in which similar reference characters refer to similar parts, there is shown a vacuum melting and casting apparatus which is espe cially designed for producing directionally solidified cast alloy components. The apparatus comprises a traveling vacuum furnace chamber, generally'designated as A, in which is'mounted a crucible B for melting and refining the alloy, and a plurality of mold chambers or lockers, generally designated as C, in which the parts are individually cast under vacuum and cooled at a controlled rate'over an extended period of time along an established temperature gradient. The furnace chamber A is guided for successive coupling to one of themold chambers C at a time so that the alloy maybe poured under vacuum and thereafter individually cooled under vacuum isolated from the furnace chamber and-from the other mold chambers.

, The melting chamber A comprises a reinforced steel housing 12 of generally rectangular configuration and of sufficient dimensions to enclose the crucible B and its supporting structure. An overhead vacuum lock 14 is included in-the top wall thereof to permit new material, such as a metal slug, to be charged into the crucible furnace B. Sight glass 16 is also incorporated in the top of the housing 12 so that charging of the crucible B and the melting of its contents may be conveniently observed by an operator standing on platform 18. The platform 18 which supports the entire furnace is itself mounted on wheels 20 guided upon and riding in straight tracks 22. The wheels 20 are mounted on axles 21 which are both laterally and rotatably slidable in bearings 23 at the underside of the platform 18. Water and power services are provided to the platform 18 through a flexible carrier 26 so that the melting chamber A may be transported down the tracks 22 to anyone of the mold chambers C. As shown, the mold chambers C are oriented in substantially a straight line. However, it is contemplated that other configurations, such as a circular or angular arrangement may be employed to suit the needs of the foundry and its available floor space. A vacuum pump 24 at the end of the line acts as the source for producing vacuum for the mold chambers C.

tions which would otherwise occur if the furnace were alternately heated and then allowed to cool appreciably while i on standby. As a consequence, cracking, flaking and/or phase changes of the refractory is minimized since extensive chilling of the furnace between melting operations does not occur.

Yet still another object of this invention is to provide a directional solidification casting apparatus which yields consistently uniform cast parts. Since rapid sequence casting In addition to being capable of transportation longitudinally along the track 22 for servicing any one of the mold chamber stations, the melting chamber A can also be transversely shifted approximately 4 to 6 inches into abutment with the adjacent mold chamber C. As best shown in FIGS. 4, 5 and 6, the transverse shifting mechanism includes a hydraulic cylinder 30 which is affixed to the underside of the platform 18 above each axle 21. The piston 31 of each cylinder 30 is connected FIG-3 is a top plan view of the melting chamber in coupled Y to a collar 32 which slidably embraces disk 33 secured to each axle 2'1. Longitudinal movement of the platform 18 is effected by hydraulic drive motor 34 operating through chain and, sprocket drive 35.

A vacuum pump 36 is connected to the rear wall of the melt chamber-A through a suitable conduit 38 and is capable of reducing the pressure within the chamber in the range of onehalf to microns. Also mounted on the platform 18 is a control console and power unit 40 which permits the operator to oversee the operations and conduct their performance from a self-contained convenient work station.

At the front of the furnace chamber A is a boxlike enclosure 42 in which is suspended a valve door 44. The valve door 44 is supported for vertical movement by cables 46 coupled to a suitable drive motor 48 mounted within the top of the enclosure 42. When lowered into a position covering the opening 50 of the furnace chamber A and urged into abutment against peripheral gasket 52 by quadrilaterally disposed latching cams 54, the reduced pressure in the chamber A acts to maintain the-valve door 44 in sealed disposition. A perimetrical flange 56 is formed about the entire margin of enclosure 42 and is adapted to be pressed into abutting disposition with the complementary marginal flange 58 and against gasket 60 thereon, both of the latter of which are arranged perimetricallly about boxlike enclosures 62 formed on each of the mold chambers The mold chambers C are each generally rectangular steel locker s, approximately to 25 of which are capable of being serviced by a single furnace. The rear wall of each locker includes a vertically suspended valve door 64 which is hung by cables 66 within the enclosure 62. The cables 66 are actuated by drive motor 68 mounted at the top of each melt chamber enclosure 62. The melt chamber valve door 64 is adapted to be lowered over the opening 70 and pressed against gasket 72 marginally disposed thereabout using four quadrilaterally arranged latching earns 74. When the pressure within the mold chamber C- is less than that within the boxlike enclosure 62, the valve door 64 which urged against the gasket 72 is hermetically sealed thereagainst the opening 70 by the cooperating external pressure.

The front of each mold chamber C has a swinging door 76 which permits loading and unloading of the molds within the chamber. A sight port 78 in each door 76 allows the moltenmetal-pouring operation from the front while a sight port 80 at the top of the mold chamber permits observation from above. Each of the mold chambers C isconnected through a manifold 82 to the line vacuum pump 24 which is capable of evacuating 6,000 to l0,000 cubic feet per minute and drawing a vacuum in the range of OYS'to 10 microns simultaneously in all casting chambers. A conventional vacuum gate valve 84 is adapted to isolate each mold chamber C from the fine vacuum manifold 82 and the remainder of the mold chambers during opening of the door 76 of any particular mold chamber. In addition, each of the mold chambers C is adapted to be coupled to a source of rough vacuum through conduit 86 and isolated therefrom by vacuum gate valve 88. The rough vacuum pump (not shown] for the coarse exhaust system is capable of drawing 300 cubic feet of air per minute to remove air from the system through conduit 86.

The molds are conventional for the directional solidification casting process and include for example an investment shell 90 into which the molten metal is poured, a chill plate 92 through which cold water is circulated to produce a temperature gradient from top to bottom, and induction or radiant healing coils 94 which encircle the investment shell mold. The molds 90 are adapted to be loaded into the respective chumbers C through the front access doors 76. The heating coils 94 finally lifted to create thermal gradients.

The crucible B includes a refractory-lined vessel which may be any of the well known electric crucibles for heating an ingot to melting temperature. The crucible B is mounted by trunnions 96 upon a reciprocable cradle 98 which projects from within the melt chamber A. As is evident from FIG. 2,

the crucible B is adapted to be extended on cradle 98 through the open hatchways 50 and 70 into the respective mold chambers C and after pouring into the molds retracted back into the furnace chamber A.

As is apparent from the foregoing description, a typical cycle of operations is as follows: A metal ingot or slug is charged into the crucible B throughthe overhead vacuum lock while the furnace chamber A is preferably evacuated, Vacuum melting and refining is commenced in the pressure range of a few, microns. If desired, final or late alloying additions may be made to the molten metal in the crucible. The furnace chamber A has in the interim been transported to a position adjacent an evacuated mold chamber which'has a preheated mold located therein. The furnace chamber is then laterally displaced until the flange 56 abuts up against the gasket 60 on flange 58. The intermediate chamber between the closed valve doors 44 and 64 is evacuated through a valved port 100 coupledto the rough manifold 86. With the pressure equalized, the latches 54 and 74 are released to permit opening of the respective valve doors 44 and 64, and the doors lifted. The crucible B is then extended through the open hatchways 50 and 70 into the mold chamber C, and the contents are poured into the mold D. The directional solidification technique is then commenced. The crucible B is immediately retracted back into the furnace chamber A and both the valve doors 44 and 64 closed. Vacuum is released within the intermediate chamber through port 100, and the furnace chamber laterally translated out of abutment with the recently poured mold-chamber. The carriage of the furnace chamber A is then driven to the next casting station C preparatory to a repetition of the sequence of operations. It is evident that the melting operations in the furnace chamber A can be performed under vacuum during transportation of the furnace carriage from one station to another without allowing appreciable'cooling of the crucible B itself. in the event that replacement of the crucible lining is required (after production of 8 to 24 heats), the melting carriage is advanced to an open position. The vacuum to the melting chamber A may then be broken through suitable valving, its'valve door 44 opened, and the crucible relined or replaced through the open hatch 50. It is also apparent that since each of the casting chambers C, 15 to 25 of which being capable of service by a single melting chamber, can be isolated from the others, the long solidification cycle can be conducted without interrupting the casting of any other molds or without infringing appreciably on melting operations.

Although this invention has been described in considerable detail, such description is intended as being illustrative rather than limiting since the invention may be variously embodied, and the scope of the invention is to be determined as claimed.

What is claimed is:

1. Vacuum melting and casting apparatus comprising a furnace chamber, crucible means for melting metal in said furnace chamber.

vacuum means for evacuating said furnace chamber,

a plurality of spaced casting chambers including molds therein, vacuum means for evacuating each of said casting chambers, I

means for transporting said furnace chamber in successive juxtaposition with each of said casting chambers, and

valve means interposed between said furnace chamber and said casting chamber in juxtaposition therewith to permit when open the pouring under vacuum of molten metal from said crucible means into the mold of said casting chamber in communication with said furnace chamber and when closed the solidification of the casting poured in said last-mentioned casting chamber isolated from the other casting chambers and from said furnace chamber.

2. Theapparatus of claim 1 wherein said valve means includes a hatchway door on said furnace chamber and a hatchway door on each of said casting chambers.

3. The apparatus of claim 2 wherein each said casting chamber hatchway door is disposed in a flanged enclosure on one side of the casting chamber and complementary with a flanged enclosure on one side of the furnace chamber 4. The apparatus of claim 3 including means to move said furnace chamber so that the flanged enclosure thereof is in abutment with the flanged enclosure on the juxtaposed casting chamber.

5. The apparatus of claim 4 including means for evacuating theintermediate space between the hatchway doors of the abutting enclosures to equalize the pressure therein with respect to the adjacent casting chamber and furnace chamber.

6. The apparatus of claim 5 including means to carry said crucible means from said furnace chamber into the adjacent casting chamber for pouring the molten metal therein into the mold in said adjacent casting chamber and thereafter retract said crucible means back into said furnace chamber.

7. The apparatus of claim 6 including a second door on each of said casting chambers for loading and unloading of molds therein.

8. The apparatus of claim 1 including a vacuum lock on said furnace chamber for charging said crucible means without breaking vacuum.

9. The apparatus of claim 1 wherein said vacuum means for evacuating said casting chamber includes a rough vacuum pump and a fine vacuum pump.

10. The apparatus of claim 1 including a heating coil in each of saidcasting chambers, and means for vertically reciprocating each of said heating coils with respect to a corresponding mold whereby the heating coils may be first lowered about said molds and then lifted at a controlled rate to effect directional solidification. 

1. Vacuum melting and casting apparatus comprising a furnace chamber, crucible means for melting metal in said furnace chamber, vacuum means for evacuating said furnace chamber, a plurality of spaced casting chambers including molds therein, vacuum means for evacuating each of said casting chambers, means for transporting said furnace chamber in successive juxtaposition with each of said casting chambers, and valve means interposed between said furnace chamber and said casting chamber in juxtaposition therewith to permit when open the pouring under vacuum of molten metal from said crucible means into the mold of said casting chamber in communication with said furnace chamber and when closed the solidification of the casting poured in said last-mentioned casting chamber isolated from the other casting chambers and from said furnace chamber.
 2. The apparatus of claim 1 wherein said valve means includes a hatchway door on said furnace chamber and a hatchway door on each of said casting chambers.
 3. The apparatus of claim 2 wherein each said casting chamber hatchway door is disposed in a flanged enclosure on one side of the casting chamber and complementary with a flanged enclosure on one side of the furnace chamber.
 4. The apparatus of claim 3 including means to move said furnace chamber so that the flanged enclosure thereof is in abutment with the flanged enclosure on the juxtaposed casting chamber.
 5. The apparatus of claim 4 including means for evacuating the intermediate space between the hatchway doors of the abutting enclosures to equalize the pressure therein with respect to the adjacent casting chamber and furnace chamber.
 6. The apparatus of claim 5 including means to carry said crucible means from said furnace chamber into the adjacent casting chamber for pouring the molten metal therein into the mold in said adjacent casting chamber and thereafter retract said crucible means back into said furnace chamber.
 7. The apparatus of claim 6 including a second door on each of said casting chambers for loading and unloading of molds therein.
 8. The apparatus of claim 1 including a vacuum lock on said furnace chamber for charging said crucible means without breaking vacuum.
 9. The apparatus of claim 1 wherein said vacuum means for evacuating said casting chamber includes a rough vacuum pump and a fine vacuum pump.
 10. The apparatus of claim 1 including a heating coil in each of said casting chambers, and means for vertically reciprocating each of said heating coils with respect to a corresponding mold whereby the heating coils may be first lowered about said molds and then lifted at a controlled rate to effect directional solidification. 